1. Field of the Invention:
The present invention relates to a lead frame by which a highly reliable semiconductor device is provided. The present invention also relates to a semiconductor device in which a semiconductor chip is packaged with a resin, as well as a manufacturing method therefor.
2. Description of the Related Art:
FIG. 1 is a plan view illustrating the relationship between a die and a lead frame with a semiconductor chip mounted thereon when the semiconductor chip is packaged with a resin. In FIG. 1, a rectangular semiconductor chip 1 is mounted on a die pad 3 located substantially at the central portion of a lead frame 8. The die pad 3 is connected to and supported through supporting leads 7 extending to outer frames 2 of the lead frame 8 which are disposed parallel to each other. A plurality of leads 4 are disposed in opposed relation with the semiconductor chip 1 on each of the long sides of the semiconductor chip 1. Each of the leads 4 includes an inner lead 4a disposed in opposed relation with the semiconductor chip 1, and an outer lead 4b extending from the end of the inner lead 4a remote from the semiconductor chip 1. The leads 4 on each of the long sides of the semiconductor chip 1 are connected with each other by a tie bar 5 at the substantially central portions thereof. Unillustrated electrode pads formed on the surface of the semiconductor chip 1 are electrically connected to the corresponding inner leads 4a by wires 6 made of, for example, gold.
Such a lead frame-semiconductor chip assembly is packaged with a resin using a mold 10. As shown in FIG. 2, the mold 10 includes an upper mold half 10a and a lower mold half 10b. The upper and lower mold halves 10a and 10b respectively have rectangular cavity halves 11a and 11b and groove-shaped gate halves 12a and 12b which communicate with the cavity halves 11a and 11b. The portions of the gate halves 12a and 12b, which serve as the entrance to the cavity halves 11a and 11b, form gate ports 13a and 13b having a rectangular cross-section.
Resin packaging will be conducted as follows. First, the semiconductor chip 1 is mounted on the die pad 3 of the lead frame 8, and this leadframe-chip assembly is carried between the upper and lower mold halves 10a and 10b and is located at a predetermined position, as shown in FIG. 1. Thereafter, the upper and lower mold halves 10a and 10b are respectively lowered and raised to sandwich the lead frame 8 therebetween, as shown in FIG. 2. At this time, the upper and lower mold halves 10a and 10b make contact with the outer frames 2 of the lead frame 8, the leads 4 and part of the hanging leads 7. Further, the cavity halves 11a and 11b in combination form a cavity 11 within the mold 10 with the semiconductor chip 1 on the die pad 3 being accommodated therein. Furthermore, the pair of gate halves 12a and 12b form a tubular gate 12, which communicates with the cavity 11 through a gate port 13 formed by the pair of gate port halves 13a and 13b.
Next, a molten thermosetting resin 14 is injected into the cavity 11 through the gate 12 formed in the mold 10 under a predetermined pressure. The resin 14 is divided into two flows by the outer frame 2 of the lead frame 8 which is disposed in such a manner that it separates part of the interior of the gate 12 into upper and lower portions. These portions guide these flows toward the gate port 13 along the upper and lower sides of the outer frame 2. Although a large part of the area within the cavity 11 is separated into upper and lower portions by the die pad 3 having the semiconductor chip 1 mounted thereon, no outer frame 2 exists in the vicinity of the gate port 13, so the resin flows 14 that have passed along the upper and lower sides of the outer frame 2 meet each other near the gate port 13. Thereafter, the resin 14 enters and fills the cavity 11, as shown by the arrows in FIG. 3.
In this state, the thermosetting resin 14 within the cavity 11 is heated to a predetermined temperature to set it. Subsequently, the upper and lower mold halves 10a and 10b are respectively raised and lowered to open the mold 10, and the leadframe-chip assembly is removed from the mold 10. Next, the leadframe-chip assembly is subjected to a subsequent process in which the tie bars 5 are cut and the leads 4 are bent, thereby completing a semiconductor device.
As stated above, although the resin 14 injected toward the cavity 11 is divided into two upper and lower flows by the outer frame 2 within the gate 12, these two flows meet each other in the vicinity of the gate port 13. Thereafter, the resin 14 is again divided into upper and lower flows to be introduced over and under the semiconductor chip 1, respectively. At this time, these new flows are, however, not always uniformly introduced over and under the chip 1. The flows generally have different resistances due to the wires 6 the positions of the semiconductor chip 1 and the die pad 3 in the cavity 11 and so on. In consequence, if the lead frame 8 is not supported so firmly by the leads 7, or if the viscosity of the resin 14 is large, the die pad 3 may be deformed or the semiconductor chip 1 misplaced because of the unbalanced flow pressure of the resin 14, as shown in FIG. 3. This may cause breaks of the wires 6 that connect the electrodes of the semiconductor chip 1 to the inner leads 4a in the resin-packaged semiconductor device. Alternatively, this may make the upper and lower portions of the packaging resin 14 with respect to the semiconductor chip 1 unequal in their thickness, thus leading to the deterioration in the moisture resistance of the semiconductor device.